NAD(P)-dependent glucose dehydrogenase (EC 1.1.1.47; hereinafter, “glucose dehydrogenase” is sometimes referred to as “GDH”, and “NAD(P)-dependent glucose dehydrogenase” as “NAD(P)-GDH”) is an enzyme that is mainly used for blood glucose concentration measurement. This catalyst catalyzes the following reaction.D-glucose+NAD(P)→D-glucono-δ-lactone+NAD(P)H 
Glucose oxidase is also known as an enzyme that can be used for blood glucose measurement. However, this enzyme is said to have a problem in that glucose concentration measurement using glucose oxidase is affected by dissolved oxygen concentration because this enzyme may use molecular oxygen as an electron acceptor. Since glucose dehydrogenase is not influenced by such dissolved oxygen, this enzyme has been used as the main enzyme for blood glucose measurement in recent years. GDH enzymes include NAD(P)-dependent GDH, pyrroloquinoline quinone (PQQ)-dependent GDH, and flavin-dependent GDH. PQQ-dependent GDH, such as Acinetobacter baumannii-derived GDH, has a problem with substrate specificity in that PQQ-dependent GDH is as reactive with maltose as it is with glucose. Examples of known flavin-dependent GDH include Aspergillus terreus-derived GDH. Flavin-dependent GDH has stricter substrate specificity than PQQ-dependent GDH. However, flavin-dependent GDH does not necessarily have sufficient substrate specificity because its reactivity with xylose is about 9% relative to that with glucose. Furthermore, flavin-dependent GDH has a temperature stability of up to approximately 50° C., which is not sufficient.
Among known types of NAD(P)-GDH, Bacillus bacteria-derived NAD(P)-GDH is well known. For example, Bacillus subtilis, Bacillus megaterium, Bacillus cereus, etc., have been reported as strains that produce GDH. Although such bacteria-derived NAD(P)-GDH has a relatively high substrate specificity, its thermal stability is up to approximately 50° C. and is thus not sufficient.
Hyperthermophilic archaea are microorganisms that are systematically classified as Archeae, and that can grow at 90° C. or higher or have an optimum growth temperature of 80° C. or higher. The enzymes derived from hyperthermophilic archaea generally have high heat resistance. Many heat-resistant enzymes have been isolated from hyperthermophilic archaea and industrially utilized. NAD(P)-GDH has also been isolated from hyperthermophilic archaea, and the characteristics thereof have been investigated. Sulforobus solfataricus-derived GDH (Non-Patent Document 1), Thermoplasma acidophilum-derived GDH (Non-Patent Document 2), and Thermoproteus tenax-derived GDH (Non-Patent Document 3) have been reported in 1986, 1989, and 1997, respectively. Although these enzymes have excellent heat resistance, they have poor substrate specificity, compared to bacteria-derived enzymes. When NADP is used as a coenzyme, Sulfolobus solfataricus-derived GDH has a broader substrate specificity, and acts on galactose or xylose more strongly than on glucose at a substrate concentration of 40 mmol/L. When NAD is used as a coenzyme, specificity of Sulfolobus solfataricus-derived GDH for glucose is relatively increased, but its activity toward xylose is still high, i.e., about 26% relative to that toward glucose. When NADP is used as a coenzyme, the activity of T. acidophilum-derived GDH toward galactose is 70% relative to that toward glucose. T. tenax-derived GDH is also highly reactive with xylose. In blood glucose concentration measurement, the use of GDH that has low substrate specificity and high reactivity with substances other than glucose results in inaccurate blood glucose measurement, and is thus extremely disadvantageous. However, NAD(P)-GDH that is derived from hyperthermophilic archaea and that has a high heat resistance of 80° C. or higher and high specificity for glucose has not been known.    Non-Patent Document 1: Giardina P et al., Biochem. J., Vol. 239, pp. 517-522 (1986)    Non-Patent Document 2: Smith L D et al., Biochem. J., Vol. 261, pp. 793-797 (1989)    Non-Patent Document 3: Siebers B et al., Arch. Microbiol., Vol. 168, pp. 120-127 (1997)